The present invention relates to current sensors and, more particularly, to a novel current sensor utilizing an isolated Hall-effect device in a closed feedback loop to provide an accurate ratioed measurement of current flowing in an adjacent conductor.
In electrical circuits, the most desirable variable for measurement and control is often the current flowing in a power circuit. It is well known that measurement of a current by causing that current to flow through a resistance, and then measuring the resulting voltage will not allow isolation of the measurement circuit from the power circuit. Typically, a current transformer is utilized to provide the isolation, although a current transformer having a high current ratio will require a large number of secondary winding turns. While normally undesirable, the use of current transformers is even more undesirable when it is necessary to measure several large currents simultaneously, as in the measurement of phase currents in a multi-phase (e.g. a three-phase) induction motor circuit, so that the three measured phase currents can be manipulated in an overload relay circuit to obtain proper motor protection.